Solar cells may be defined as devices for converting light energy into electric energy by using a photovoltaic effect of generating electrons when light is incident onto a P-N junction diode. The solar cell may be classified into a silicon solar cell, a compound semiconductor solar cell mainly including a group I-III-VI compound or a group III-V compound, a dye-sensitized solar cell, and an organic solar cell according to materials constituting the junction diode.
A solar cell made from CIGS (CuInGaSe), which is one of group I-III-VI Chal-copyrite-based compound semiconductors, represents superior light absorption, higher photoelectric conversion efficiency with a thin thickness, and superior electro-optic stability, so the CIGS solar cell is spotlighted as a substitute for a conventional silicon solar cell.
In general, a CIGS thin film solar cell is fabricated by sequentially forming a substrate having sodium (Na), a back electrode layer, a light absorbing layer, a buffer layer, and a front electrode layer. In general, the back electrode layer is made of molybdenum (Mo), and heat treatment is performed at a temperature of 450° C. or above in the selenium (Se) atmosphere so that a MoSe2 layer is formed. The MoSe2 layer functions as an electrode, and reduces damage applied to a molybdenum electrode during a patterning process.